This invention relates to the field of microelectronic optical lithography and more particularly to a method and apparatus for the construction of very large solid state electronic devices sometimes known as VLSI devices.
Prior art optical lithography techniques which are used to produce patterned wafers may be briefly described as follows. A chip pattern is used to fabricate a reticle. The reticle is then placed beneath a source of light, with the light being projected through the reticle (embodying the chip pattern therein) and onto one portion of a wafer, such as a silicon wafer. To make a second chip pattern, the wafer is stepped or indexed relative to the reticle and the source of light, and the process repeated. This continues until the entire usable area of the wafer is exhausted, i.e., completely filled with the chip patterns.
Alternatively, the reticle formed from the original chip pattern may be placed in a step and repeat camera to thereby make a plurality of identical chip patterns on a mask. The mask is then developed and placed in a contact printer. The printer then contacts the wafer, with the same end result. Since contact printing rapidly destroys the mask, a one-to-one projection printer is preferred in mass production.
This process is now repeated for each of the several etching steps which are usually required to produce a patterned wafer. At the completion of this process, the patterned wafer, now containing a plurality of identical chip patterns over its surface with each chip pattern being the result of a plurality of etching, ion implantation, coating, etc. operations, is diced. This dicing results in a plurality of chips of identical electrical and geometrical properties. Such a process is described in an article entitled Electron Lithography for the Fabrication of Mic roelectric Devices, page 800, et seq., by Geraint Owen, Rep. Prog. Phys. Vol. 48, pp. 795-851, 1985, hereby incorporated by reference.
To make, for example a microcomputer, a chip is placed in a carrier and a plurality of chip carriers are placed on a card, there being suitable electrical connections between the chips of each chip carrier. Typically, a microcomputer consists of a plurality of cards mounted on a board with electrical connections existing between and into the various cards. (The monitor, usually a CRT, is a separate opto-electronic entity.)
Clearly, the use of a plurality of cards and the necessity of mounting a plurality of chip carriers on each card entails significant and expensive operations and techniques.